Fix the default checksum algorithm in the manpage

The manpage reports fletcher2, but in zio.h ZIO_CHECKSUM_ON_VALUE
is defined to ZIO_CHECKSUM_FLETCHER_4.

Signed-off-by: Massimo Maggi <me@massimo-maggi.eu>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes #1628
Fix man page for the sync property

The help output of for zfs set/get says that sync can be one of

  standard | always | disabled

but the man pages claim it can be

  sync=default | always | disabled

the accepted value is standard, this changes the manpage to give the
correct values.

Signed-off-by: Steven Burgess <sburgess@dattobackup.com>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes #1634
Write dirty inodes on close

When the property atime=on is set operations which only access
and inode do cause an atime update.  However, it turns out that
dirty inodes with updated atimes are only written to disk when
the inodes get evicted from the cache.  Somewhat surprisingly
the source suggests that this isn't a ZoL specific issue.

This behavior may in part explain why zfs's reclaim logic has
been observed to be slow.  When reclaiming inodes its likely
that they have a dirty atime which will force a write to disk.

Obviously we don't want to force a write to disk for every
atime update, these needs to be batched.  The right way to
do this is to fully implement the .dirty_inode and .write_inode
callbacks.  However, to do that right requires proper unification
of some fields in the znode/inode.  Then we could just mark the
inode dirty and leave it to the VFS to call .write_inode
periodically.

Until that work gets done we have to settle for some middle
ground.  The simplest and safest thing we can do for now is
to write the dirty inode on last close.  This should prevent
the majority of inodes in the cache from having dirty atimes
and not drastically increase the number of writes.

Some rudimentally testing to show how long it takes to drop
500,000 inodes from the cache shows promising results.  This
is as expected because we're no longer do lots of IO as part
of the eviction, it was done earlier during the close.

w/out patch: ~30s to drop 500,000 inodes with drop_caches.
with patch:  ~3s to drop 500,000 inodes with drop_caches.

Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Illumos #3639 zpool.cache should skip over readonly pools

3639 zpool.cache should skip over readonly pools
Reviewed by: Eric Schrock <eric.schrock@delphix.com>
Reviewed by: Adam Leventhal <ahl@delphix.com>
Reviewed by: Basil Crow <basil.crow@delphix.com>
Approved by: Gordon Ross <gwr@nexenta.com>

References:
  illumos/illumos-gate@fb02ae025247e3b662600e5a9c1b4c33ecab7d72
  https://www.illumos.org/issues/3639

Normally we don't list pools that are imported read-only in the cache
file, however you can accidentally get one into the cache file by
importing and exporting a read-write pool while a read-only pool is
imported:

$ zpool import -o readonly test1
$ zpool import test2
$ zpool export test2
$ zdb -C

This is a problem because if the machine reboots we import all pools in
the cache file as read-write.

Ported-by: Richard Yao <ryao@gentoo.org>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Return correct type and offset from zfs_readdir

zfs_readdir() is used by getdents(), which provides a list of all files
in directory, their types and an offset that be used by llseek() to seek
to the next directory entry.

On Solaris, the first two directory entries "." and ".." respectively
have offsets 1 and 2 on ZFS while the other files have rather large
numbers. Currently, ZFSOnLinux is  giving "." offset 0 and all other
entries large numbers. The first entry's next entry offset points to
itself, which causes software that uses llseek() in conjunction with
getdents() for filesystem navigation to enter an infinite loop.  The
offsets used for each directory entry are filesystem specific on all
platforms, so we can fix this by adopting the Solaris behavior.

Also, we currently report each directory entry as having type 0 (???).
This is not wrong, but we can do better. getdents() on Solaris does not
appear to provide this information, but it does on Linux and Mac OS X
do. ZFS provides easy access to type information in zfs_readdir(), so
this patch provides this as well.

Reported-by: Andrey <andrey@kudinov.su>
Signed-off-by: Richard Yao <ryao@gentoo.org>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes #1624
Return -1 from arc_shrinker_func()

This is analogous to SPL commit zfsonlinux/spl@b9b3715.  While
we don't have clear evidence of systems getting caught here
indefinately like in the SPL this ensures that it will never
happen.

Signed-off-by: Richard Yao <ryao@gentoo.org>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes #1579
Illumos #3137 L2ARC compression

3137 L2ARC compression
Reviewed by: George Wilson <george.wilson@delphix.com>
Reviewed by: Matthew Ahrens <mahrens@delphix.com>
Approved by: Dan McDonald <danmcd@nexenta.com>

References:
  illumos/illumos-gate@aad02571bc59671aa3103bb070ae365f531b0b62
  https://www.illumos.org/issues/3137
  http://wiki.illumos.org/display/illumos/L2ARC+Compression

Notes for Linux port:

A l2arc_nocompress module option was added to prevent the
compression of l2arc buffers regardless of how a dataset's
compression property is set.  This allows the legacy behavior
to be preserved.

Ported by: James H <james@kagisoft.co.uk>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes #1379
Illumos #3964 L2ARC should always compress metadata buffers

3964 L2ARC should always compress metadata buffers
Reviewed by: Matthew Ahrens <mahrens@delphix.com>
Reviewed by: Brian Behlendorf <behlendorf1@llnl.gov>

References:
  https://www.illumos.org/issues/3964

Ported-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes #1379
Allow arc_evict_ghost() to only evict meta data

The default behavior of arc_evict_ghost() is to start by evicting
data buffers.  Then only if the requested number of bytes to evict
cannot be satisfied by data buffers move on to meta data buffers.

This is ideal for honoring arc_c since it's preferable to keep the
meta data cached.  However, if we're trying to free memory from the
arc to honor the meta limit it's a problem because we will need to
discard all the data to get to the meta data.

To avoid this issue the arc_evict_ghost() is now passed a fourth
argumented describing which buffer type to start with.  The
arc_evict() function already behaves exactly like this for a
same reason so this is consistent with the existing code.

All existing callers have been updated to pass ARC_BUFC_DATA so
this patch introduces no functional change.  New callers may
pass ARC_BUFC_METADATA to skip immediately to evicting meta
data leaving the normal data untouched.

Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Evict meta data from ghost lists + l2arc headers

When the meta limit is exceeded the ARC evicts some meta data
buffers from the mfu+mru lists.  Unfortunately, for meta data
heavy workloads it's possible for these buffers to accumulate
on the ghost lists if arc_c doesn't exceed arc_size.

To handle this case arc_adjust_meta() has been entended to
explicitly evict meta data buffers from the ghost lists in
proportion to what was evicted from the mfu+mru lists.

If this is insufficient we request that the VFS release
some inodes and dentries.  This will result in the release
of some dnodes which are counted as 'other' metadata.

Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Linux 3.8 compat: Support CONFIG_UIDGID_STRICT_TYPE_CHECKS

When CONFIG_UIDGID_STRICT_TYPE_CHECKS is enabled uid_t/git_t are
replaced by kuid_t/kgid_t, which are structures instead of integral
types. This causes any code that uses an integral type to fail to build.
The User Namespace functionality introduced in Linux 3.8 requires
CONFIG_UIDGID_STRICT_TYPE_CHECKS, so we could not build against any
kernel that supported it.

We resolve this by converting between the new kuid_t/kgid_t structures
and the original uid_t/gid_t types.

Signed-off-by: Richard Yao <ryao@gentoo.org>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes #1589